The present invention generally relates to live roller accumulation conveyors used to transport articles along a predetermined conveying path and, more particularly, to product-detecting trigger assemblies that can be advantageously used in zero pressure accumulation conveyors.
Live roller accumulation conveyors are well known in the art and have employed various mechanisms for controlling the drive to their powered carrier rollers to allow those carrier rollers to be selectively rotated or stopped to accommodate accumulation of the articles being conveyed. Typically, the carrier rollers are belt driven and convey the articles to a collection or accumulation location and, once one or more of the articles have reached that location or those locations, the power to an upstream group of carrier rollers is stopped to provide for accumulation.
One such conveyor and control mechanism is shown in my U.S. Pat. No. 5,016,748. That patent discloses an accumulation conveyor that includes a frame having two generally parallel sides. A plurality of carrier rollers are rotatably mounted between the parallel side frame members and are driven by a drive belt. A plurality of trigger assemblies are also mounted to the sides of the frame. Each trigger assembly includes two opposing pivot brackets pivotally mounted on each end of the shaft of a selected carrier roller, which forms the pivot axis for the trigger assembly. Each trigger assembly further includes a single sensing roller mounted on the opposing pivot brackets on one side of the trigger assembly pivot axis and a counterbalance roller, which is heavier than the sensing roller, is mounted on the opposite side of the trigger assembly pivot axis. The counterweight roller biases its associated sensing roller into the path of movement of articles transported along the conveyor bed. The trigger assembly actuates and deactuates a switch associated with an air valve for selective application of the drive belt to the carrier rollers upstream of the trigger assembly based upon the detection of articles by the sensing roller of the trigger assembly.
Although the trigger assembly disclosed in the aforementioned patent is suitable for use in the conveyance of many articles which are conveyed by conveyor systems, the assembly disclosed therein has a deficiency which is most apparent when the articles being conveyed by the accumulation conveyor have irregular bottom surfaces, tapered ends and/or flanges. These tapered ends and/or flanges of a conveyed article can produce gaps between a particular conveyed article and other conveyed articles during accumulation. On occasion, the irregular bottom surfaces or the gaps resulting from tapered ends and/or flanges allow the sensing roller of the single sensor trigger assembly disclosed in U.S. Pat. No. 5,016,748, to raise above the conveying surface even when an article is being conveyed thereover. In turn, the counterweight roller associated with that trigger assembly remains in its lowered position and does not actuate the switch of its associated air valve. This prevents the accumulation of articles in the zone immediately upstream from that trigger assembly and causes undesirable line pressure, thereby effectively eliminating the zero pressure accumulation characteristic of the conveyor.
Several attempts have been made to overcome this deficiency common to single sensor trigger assemblies. For example, a first common practice to overcome this deficiency has involved a mechanical linkage system that links two such single sensor trigger assemblies together. In this arrangement, when one of the trigger assemblies pivots, its linked trigger assembly also pivots. As a result, the switches of the air valves respectively associated with those trigger assemblies are actuated if either of the sensing rollers associated with those single sensor trigger assemblies detect the presence of an article.
This first solution to the deficiency common to ordinary single sensor trigger assemblies has been less than satisfactory because it requires the use of additional components to the conveyor system, thereby increasing production and maintenance costs of the system. Also, because, in this arrangement, a transported article must overcome the bias of two counterweight rollers, a conveyor system utilizing this potential solution is not well suited for accumulating lightweight articles. Moreover, this solution inherently decreases article throughput because the deactuation of each zone may be induced by the deactuation of its linked zone. In this regard, articles might be accumulated at alternating zones rather than at each zone.
Another solution to the deficiency of ordinary single sensor trigger assemblies is to pneumatically couple two or more of the air valves positioned in adjacent conveyor zones so that actuation of a switch associated with either air valve initiates the accumulation process for the other such valve.
This second solution requires additional pneumatic components in the conveyor system and therefore increases its production costs, maintenance costs and complexity. Moreover, this solution inherently decreases article throughput because the deactuation of each zone may be induced by the deactuation of its coupled zone. In this regard, articles might be accumulated at alternating zones rather than at each zone. As such, this second solution is not well suited for many uses.
A third known solution to overcome the deficiency of single sensor trigger assemblies is to replace mechanical trigger assemblies with optically actuated sensor assemblies, such as those that utilize one or more photo-electric sensors. The use of optical technologies, such as photo-electric sensors, however, increases the production and maintenance costs of a conveyor system. Furthermore, these systems are more complex and require more supervision. As such, this third solution is not well suited for many applications.
A zero pressure accumulation conveyor utilizing the dual sensor trigger assembly of the present invention overcomes the aforementioned disadvantages of the prior art. In particular, a zero pressure accumulation conveyor utilizing a trigger assembly constructed in accordance with the principles of the present invention eliminates concern with regard to the conveyance of articles having irregular bottom surfaces, tapered ends and/or flanges. Such a trigger assembly is safe and quiet in operation and simple in construction, thereby substantially minimizing the production and maintenance costs of a conveyor system utilizing this technology. The present invention is much less complex than the aforementioned solutions to the deficiency common to ordinary single sensor trigger assemblies. As such, the present invention represents a cost efficient and effective solution to this problem.
In accordance with an important aspect of the present invention, the dual sensor trigger assembly of the present invention is a single assembly having two sensing rollers which share a common counterweight. Two carrier-type rollers are included as component parts of the trigger assembly and both are positioned adjacent to their respectively associated sensing rollers so that the shaft of each provides a pivot axis for its associated sensing roller. The pivoting of either sensing roller about the shaft of its adjacent carrier-type roller during reciprocation of the sensing roller between its biased position and its loaded position elevates or lowers the common counterweight and removes or exerts pressure from or on the actuating switch (e.g. air valve actuator in pneumatically controlled systems) associated with the trigger assembly. This deactuates or actuates the power to upstream carrier rollers to initiate or conclude an accumulation cycle, as the case may be.